A process of discovering a Wireless Local Area Network (WLAN) Access Point (AP) should be pre-performed to allow a terminal to use a WLAN service. Such a process of discovering the WLAN AP may be largely divided into two methods such as passive scanning and active scanning.
The passive scanning corresponds to a method in which a User Equipment (UE) receives a beacon frame which a WLAN AP periodically (for example, generally 100 ms) transmits and identifies the existence of the WLAN AP. At this time, for example, a maximum duration of 100 ms is required per channel according to a time point when the terminal acquires the beacon frame.
Next, the active scanning corresponds to a method in which, when the UE directly transmits a probe request frame to an AP and the AP receives the probe request frame, the AP transmits a probe response frame to the UE to inform the UE of the existence of the AP itself. The method takes little time to discover the AP per channel compared to the passive scanning, but the UE should generate the probe request frame and transmit the probe request frame to the AP, which acts as a burden to the terminal. Further, there is another burden in that the AP should generate a packet in addition to the beacon frame.
FIG. 1 illustrates a relation between throughput and overload of the UE according to the number of terminals which access one WLAN AP.
Since the UE cannot know how much of a network load the AP has before accessing (attaching) the WLAN AP, it is difficult to guarantee good performance. For example, as illustrated in FIG. 1A, as the number of UEs, which access one WLAN Access Point (AP) increases, it is noted that throughput of each UE rapidly decreases. Further, as illustrated in FIG. B, as the number of UEs, which access one WLAN AP increases, it is noted that a ratio of overload of the AP increases. As described above, if a new UE accesses an overloaded AP, which many UEs have already accessed and thus has a large loads, both the existing UEs and the new UE may have a serious performance deterioration problem.
Accordingly, one AP should not accept access of a predetermined number or more of UEs, or access of UEs should be distributed to APs that use different channels. In order to solve the above problem, an IEEE 802.11 standard document published in 2012 has added a function by which the UE can identify loads of the AP before accessing the WLAN AP through an element of “Basic Service Set (BSS) load” added to a beacon or probe response frame. However, such a method still has a burden in that the UE should receive and decode the beacon or probe response frame, so that the basic limitation, which cannot reduce the time to discover the WLAN AP, still exists.
As described above, the WLAN AP installed by a network service provider may not be sufficiently used, the UE may access the overloaded AP, and power consumption of the UE may increase due to unnecessary WLAN AP scanning.